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Advances in Therapy Feb 2021Renal tubular acidosis (RTA) occurs when the kidneys are unable to maintain normal acid-base homeostasis because of tubular defects in acid excretion or bicarbonate ion... (Review)
Review
Renal tubular acidosis (RTA) occurs when the kidneys are unable to maintain normal acid-base homeostasis because of tubular defects in acid excretion or bicarbonate ion reabsorption. Using illustrative clinical cases, this review describes the main types of RTA observed in clinical practice and provides an overview of their diagnosis and treatment. The three major forms of RTA are distal RTA (type 1; characterized by impaired acid excretion), proximal RTA (type 2; caused by defects in reabsorption of filtered bicarbonate), and hyperkalemic RTA (type 4; caused by abnormal excretion of acid and potassium in the collecting duct). Type 3 RTA is a rare form of the disease with features of both distal and proximal RTA. Accurate diagnosis of RTA plays an important role in optimal patient management. The diagnosis of distal versus proximal RTA involves assessment of urinary acid and bicarbonate secretion, while in hyperkalemic RTA, selective aldosterone deficiency or resistance to its effects is confirmed after exclusion of other causes of hyperkalemia. Treatment options include alkali therapy in patients with distal or proximal RTA and lowering of serum potassium concentrations through dietary modification and potential new pharmacotherapies in patients with hyperkalemic RTA including newer potassium binders.
Topics: Acidosis, Renal Tubular; Bicarbonates; Humans; Hyperkalemia; Kidney; Potassium
PubMed: 33367987
DOI: 10.1007/s12325-020-01587-5 -
Pediatric Clinics of North America Feb 2019Renal tubular acidosis should be suspected in poorly thriving young children with hyperchloremic and hypokalemic normal anion gap metabolic acidosis, with/without... (Review)
Review
Renal tubular acidosis should be suspected in poorly thriving young children with hyperchloremic and hypokalemic normal anion gap metabolic acidosis, with/without syndromic features. Further workup is needed to determine the type of renal tubular acidosis and the presumed etiopathogenesis, which informs treatment choices and prognosis. The risk of nephrolithiasis and calcinosis is linked to the presence (proximal renal tubular acidosis, negligible stone risk) or absence (distal renal tubular acidosis, high stone risk) of urine citrate excretion. New formulations of slow-release alkali and potassium combination supplements are being tested that are expected to simplify treatment and lead to sustained acidosis correction.
Topics: Acidosis, Renal Tubular; Child; Diagnosis, Differential; Humans; Risk Factors
PubMed: 30454739
DOI: 10.1016/j.pcl.2018.08.011 -
Indian Journal of Pediatrics Sep 2020Renal tubular acidosis (RTA) comprises a group of disorders characterized by low capacity for net acid excretion and persistent hyperchloremic metabolic acidosis,... (Review)
Review
Renal tubular acidosis (RTA) comprises a group of disorders characterized by low capacity for net acid excretion and persistent hyperchloremic metabolic acidosis, despite preserved glomerular filtration rate. RTA are classified into chiefly three types (1, 2 and 4) based on pathophysiology and clinical and laboratory characteristics. Most patients have primary RTA that presents in infancy with polyuria, growth retardation, rickets and/or hypotonia. Diagnosis requires careful evaluation, including exclusion of other entities that can cause acidosis. A variety of tests, administered stepwise, are useful for the diagnosis and characterization of RTA. A genetic or acquired basis can be determined in majority of patients through focused evaluation. Management involves correction of acidosis and dyselectrolytemia; patients with proximal RTA with Fanconi syndrome and rickets require additional supplements of phosphate and vitamin D.
Topics: Acidosis; Acidosis, Renal Tubular; Fanconi Syndrome; Glomerular Filtration Rate; Humans; Phosphates
PubMed: 32591997
DOI: 10.1007/s12098-020-03318-8 -
Pediatric Clinics of North America Feb 2019Fanconi syndrome, also known as the DeToni, Debré, Fanconi syndrome is a global dysfunction of the proximal tubule characterized by glucosuria, phosphaturia,... (Review)
Review
Fanconi syndrome, also known as the DeToni, Debré, Fanconi syndrome is a global dysfunction of the proximal tubule characterized by glucosuria, phosphaturia, generalized aminoaciduria, and type II renal tubular acidosis. Often there is hypokalemia, sodium wasting, and dehydration. In children, it typically is caused by inborn errors of metabolism, principally cystinosis. In adults, it is mainly caused by medications, exogenous toxins, and heavy metals. Treatment consists of treating the underlying cause and replacing the lost electrolytes and volume.
Topics: Child; Diagnosis, Differential; Fanconi Syndrome; Humans
PubMed: 30454741
DOI: 10.1016/j.pcl.2018.09.002 -
Nature Reviews. Nephrology Jun 2023The kidneys have a central role in the control of acid-base homeostasis owing to bicarbonate reabsorption and production of ammonia and ammonium in the proximal tubule... (Review)
Review
The kidneys have a central role in the control of acid-base homeostasis owing to bicarbonate reabsorption and production of ammonia and ammonium in the proximal tubule and active acid secretion along the collecting duct. Impaired acid excretion by the collecting duct system causes distal renal tubular acidosis (dRTA), which is characterized by the failure to acidify urine below pH 5.5. This defect originates from reduced function of acid-secretory type A intercalated cells. Inherited forms of dRTA are caused by variants in SLC4A1, ATP6V1B1, ATP6V0A4, FOXI1, WDR72 and probably in other genes that are yet to be discovered. Inheritance of dRTA follows autosomal-dominant and -recessive patterns. Acquired forms of dRTA are caused by various types of autoimmune diseases or adverse effects of some drugs. Incomplete dRTA is frequently found in patients with and without kidney stone disease. These patients fail to appropriately acidify their urine when challenged, suggesting that incomplete dRTA may represent an intermediate state in the spectrum of the ability to excrete acids. Unrecognized or insufficiently treated dRTA can cause rickets and failure to thrive in children, osteomalacia in adults, nephrolithiasis and nephrocalcinosis. Electrolyte disorders are also often present and poorly controlled dRTA can increase the risk of developing chronic kidney disease.
Topics: Adult; Child; Humans; Acidosis, Renal Tubular; Kidney Calculi; Kidney Tubules, Proximal; Forkhead Transcription Factors; Vacuolar Proton-Translocating ATPases
PubMed: 37016093
DOI: 10.1038/s41581-023-00699-9 -
Minerva Endocrinologica Dec 2019Metabolic acidosis is defined as a pathologic process that, when unopposed, increases the concentration of hydrogen ions (H+) in the body and reduces the bicarbonate... (Review)
Review
Metabolic acidosis is defined as a pathologic process that, when unopposed, increases the concentration of hydrogen ions (H+) in the body and reduces the bicarbonate (HCO3-) concentration. Metabolic acidosis can be of a kidney origin or an extrarenal cause. Assessment of urinary ammonium excretion by calculating the urine anion gap or osmolal gap is a useful method to distinguish between these two causes. Extrarenal processes include increased endogenous acid production and accelerated loss of bicarbonate from the body. Metabolic acidosis of renal origin is due to a primary defect in renal acidification with no increase in extrarenal hydrogen ion production. This situation can occur because either the renal input of new bicarbonate is insufficient to regenerate the bicarbonate lost in buffering endogenous acid as with distal renal tubular acidosis (RTA) or the RTA of renal insufficiency, or the filtered bicarbonate is lost by kidney wasting as in proximal RTA. In either condition, because of loss of either NaHCO3 (proximal RTA) or NaA (distal RTA), effective extracellular volume is reduced and as a result the avidity for chloride reabsorption derived from the diet is increased and results in a hyperchloremic normal gap metabolic acidosis. The RTA of renal insufficiency is also characterized by a normal gap acidosis, however, with severe reductions in the glomerular filtration rate an anion gap metabolic acidosis eventually develops.
Topics: Acid-Base Equilibrium; Acidosis; Acidosis, Renal Tubular; Aldosterone; Ammonia; Bicarbonates; Buffers; Chlorides; Diarrhea; Glomerular Filtration Rate; Humans; Hypokalemia; Kidney; Kidney Tubules; Models, Biological; Postoperative Complications; Protons; Renal Insufficiency, Chronic; Urinary Diversion
PubMed: 31347344
DOI: 10.23736/S0391-1977.19.03059-1 -
Nephrology, Dialysis, Transplantation :... Jul 2022Glucose levels are tightly regulated at all times. Gluconeogenesis is the metabolic pathway dedicated to glucose synthesis from non-hexose precursors. Gluconeogenesis is... (Review)
Review
Glucose levels are tightly regulated at all times. Gluconeogenesis is the metabolic pathway dedicated to glucose synthesis from non-hexose precursors. Gluconeogenesis is critical for glucose homoeostasis, particularly during fasting or stress conditions. The renal contribution to systemic gluconeogenesis is increasingly recognized. During the post-absorptive phase, the kidney accounts for ∼40% of endogenous gluconeogenesis, occurring mainly in the kidney proximal tubule. The main substrate for renal gluconeogenesis is lactate and the process is regulated by insulin and cellular glucose levels, but also by acidosis and stress hormones. The kidney thus plays an important role in the maintenance of glucose and lactate homoeostasis during stress conditions. The impact of acute and chronic kidney disease and proximal tubular injury on gluconeogenesis is not well studied. Recent evidence shows that in both experimental and clinical acute kidney injury, impaired renal gluconeogenesis could significantly participate in systemic metabolic disturbance and thus alter the prognosis. This review summarizes the biochemistry of gluconeogenesis, the current knowledge of kidney gluconeogenesis, its modifications in kidney disease and the clinical relevance of this fundamental biological process in human biology.
Topics: Gluconeogenesis; Glucose; Humans; Insulin; Kidney; Lactates
PubMed: 33247734
DOI: 10.1093/ndt/gfaa302 -
Journal of Nephrology Dec 2021Renal tubular acidosis (RTA) comprises a group of disorders in which excretion of hydrogen ions or reabsorption of filtered HCO is impaired, leading to chronic metabolic... (Review)
Review
Renal tubular acidosis (RTA) comprises a group of disorders in which excretion of hydrogen ions or reabsorption of filtered HCO is impaired, leading to chronic metabolic acidosis with normal anion gap. In the current review, the focus is placed on the most common type of RTA, Type 1 RTA or Distal RTA (dRTA), which is a rare chronic genetic disorder characterized by an inability of the distal nephron to secrete hydrogen ions in the presence of metabolic acidosis. Over the years, knowledge of the molecular mechanisms behind acid secretion has improved, thereby greatly helping the diagnosis of dRTA. The primary or inherited form of dRTA is mostly diagnosed in infancy, childhood, or young adulthood, while the acquired secondary form, as a consequence of other disorders or medications, can happen at any age, although it is more commonly seen in adults. dRTA is not as "benign" as previously assumed, and can have several, highly variable long-term consequences. The present review indeed reports and summarizes both clinical symptoms and diagnosis, long-term outcomes, genetic inheritance, epidemiology and current treatment options, with the aim of shedding more light onto this rare disorder. Being a chronic condition, dRTA also deserves attention in the transition between pediatric and adult nephrology care, and as a rare disease it has a place in the European and Italian rare nephrological diseases network.
Topics: Acid-Base Equilibrium; Acidosis, Renal Tubular; Adult; Biological Transport; Child; Humans; Young Adult
PubMed: 33770395
DOI: 10.1007/s40620-021-01032-y -
European Journal of Medical Genetics Aug 2022Nutritional vitamin D deficiency is the most frequent cause of rickets followed by genetic causes, that include entities like classic hypophosphatemic rickets (FGF23...
Nutritional vitamin D deficiency is the most frequent cause of rickets followed by genetic causes, that include entities like classic hypophosphatemic rickets (FGF23 related), Dent disease, Fanconi syndrome, renal tubular acidosis, and vitamin D dependent rickets. Hypophosphatemia is a feature in all these forms. The diagnosis relies on a combination of clinical, biochemical and radiological features, but genetic testing is required to confirm the diagnosis. We screened 66 patients with hypophosphatemic rickets referred to this center between May 2015 and July 2019 using whole exome sequencing (WES) in addition to the measurement of their intact serum fibroblast growth factor 23 (FGF23) levels. WES revealed 36 pathogenic and 28 likely pathogenic variants in 16 different genes (PHEX, FGF23, DMP1, ENPP1, CLCN5, CTNS, SLC2A2, GATM, SLC34A1, EHHADH, SLC4A1, ATP6V1B1, ATP6V0A4, CYP27B1, VDR and FGFR1) in 63 patients which helped differentiate between the various forms of hypophosphatemic rickets. Intact serum FGF23 levels were significantly higher in patients with variations in PHEX, FGF23, DMP1 or ENPP1 genes. The major genetic causes of rickets were classic hypophosphatemic rickets with elevated FGF23 levels, distal renal tubular acidosis, and vitamin D dependent rickets. Based on the present results, we propose a customized gene panel for targeted exome sequencing, which will be useful for confirming the diagnosis in most patients with hypophosphatemic rickets.
Topics: Acidosis, Renal Tubular; Familial Hypophosphatemic Rickets; Fibroblast Growth Factors; Humans; PHEX Phosphate Regulating Neutral Endopeptidase; Rickets, Hypophosphatemic; Vacuolar Proton-Translocating ATPases; Vitamin D
PubMed: 35738466
DOI: 10.1016/j.ejmg.2022.104540 -
Journal of the American Society of... Feb 2021The kidney plays an important role in maintaining normal blood pH. Metabolic acidosis (MA) upregulates the pathway that mitochondria in the proximal tubule (PT) use to...
BACKGROUND
The kidney plays an important role in maintaining normal blood pH. Metabolic acidosis (MA) upregulates the pathway that mitochondria in the proximal tubule (PT) use to produce ammonia and bicarbonate from glutamine, and is associated with AKI. However, the extent to which MA causes AKI, and thus whether treating MA would be beneficial, is unclear.
METHODS
Gavage with ammonium chloride induced acute MA. Multiphoton imaging of mitochondria (NADH/membrane potential) and transport function (dextran/albumin uptake), oxygen consumption rate (OCR) measurements in isolated tubules, histologic analysis, and electron microscopy in fixed tissue, and urinary biomarkers (KIM-1/clara cell 16) assessed tubular cell structure and function in mouse kidney cortex.
RESULTS
MA induces an acute change in NAD redox state (toward oxidation) in PT mitochondria, without changing the mitochondrial energization state. This change is associated with a switch toward complex I activity and decreased maximal OCR, and a major alteration in normal lipid metabolism, resulting in marked lipid accumulation in PTs and the formation of large multilamellar bodies. These changes, in turn, lead to acute tubular damage and a severe defect in solute uptake. Increasing blood pH with intravenous bicarbonate substantially improves tubular function, whereas preinjection with the NAD precursor nicotinamide (NAM) is highly protective.
CONCLUSIONS
MA induces AKI changes in PT NAD and lipid metabolism, which can be reversed or prevented by treatment strategies that are viable in humans. These findings might also help to explain why MA accelerates decline in function in CKD.
Topics: Acidosis; Acute Kidney Injury; Animals; Disease Models, Animal; Kidney Cortex; Kidney Tubules; Lipid Metabolism; Male; Mice; Mice, Inbred C57BL; Mitochondria; NAD; Oxygen Consumption
PubMed: 33478973
DOI: 10.1681/ASN.2020071003